But Hulot suggested that Macron's government has paid little more than lip service to environmental issues. He highlighted, for example, the government's pledges to cut back reliance on nuclear energy to 50 percent by 2025 and to curb the use of pesticides, and said there had been little progress on several other initiatives.

French President Emmanuel Macron (right) even planted a tree on the White House lawn with US President Donald Trump (center), with some observers saying it was a jab at Washington's approach to climate change

Who is Nicolas Hulot? Dubbed "France's most famous environmental activist," Hulot is a longtime campaigner for green policies and a former TV celebrity. Past French presidents, including Francois Hollande and Nicolas Sarkozy, had approached him for the Environment Ministry. However, he rejected offers to join the government until Emmanuel Macron came along.

Hulot has consistently scored high in popularity polls, even after Macron's approval ratings started to plunge. An Ifop poll suggested that 64 percent of French nationals have a favorable opinion of Hulot.

Government spokesman Benjamin Griveaux told BFM news channel that Hulot should have warned Macron and Prime Minister Edouard Philippe before announcing his resignation.

"Do you do an environmental revolution in one year? The response is no," said Griveaux. "I prefer little steps to not moving."

Observers have suggested that Hulot's departure could cause further shakeup within the government and prompt Macron to reshuffle his cabinet.

The ugly face of plastic pollution

The age of plastic

Plastic is lightweight, durable — and wildly popular. We've produced 8.3 billion metric tons of the material since mass production began in the 1950s. Because it doesn't easily biodegrade, much of what we've made now lives in landfills like this one on Nairobi's outskirts. Rubbish pickers there hunt for recyclable plastics to earn a living. But a lot of plastic also ends up in the ocean ...

The ugly face of plastic pollution

Rivers of plastic

Some 90 percent of plastic enters marine habitats via just 10 rivers: The Yangtze, the Indus, Yellow River, Hai River, the Nile, the Ganges, Pearl River, Amur River, the Niger, and the Mekong. These rivers run through highly populated areas with a lack of adequate waste disposal infrastructure. Here, a fisherman in the Philippines removes a fish and crab trap from plastic-filled waters.

The ugly face of plastic pollution

A plastic welcome to the world

Some animals have found uses for plastic waste. This swan nested in garbage on a Copenhagen lake that is popular with tourists. Her cygnets hatched surrounded by waste. It's not the best start to life. But for some animals the consequences are much worse ...

The ugly face of plastic pollution

Deadly consequences

Although plastic is highly durable and can be used for products with a long lifespan, such as furniture and piping, about 50 percent goes to disposable products, including single-use cutlery and six pack rings that end up in the natural environment. Animals, like this penguin, are in danger of becoming entangled and dying as a result.

The ugly face of plastic pollution

Eating plastic

Other animals mistake the material for food. This albatross chick was found dead on Sand Island in Hawaii with multiple pieces of plastic in its stomach. According to one study of 34 seabird species in northern Europe, Russia, Iceland, Svalbard, the Faroe Islands, Scandinavia and Greenland, 74 percent had ingested plastic. Eating the material can lead to organ damage and blockages in the gut.

The ugly face of plastic pollution

Whale killer

Even larger animals aren't immune to the effects of consuming plastic. This whale was found struggling to breathe and swim in a Thai canal. As rescuers attempted to save the animal, it vomited five plastic bags and later died. During the necropsy, vets found 80 shopping bags and other plastic garbage had clogged up the whale's stomach, so the marine creature could no longer digest nutritious food.

The ugly face of plastic pollution

Visible and invisible plastic

We're well aware of the large pieces of plastic bobbing on the ocean's surface, as is pictured here off the Hawaiian coast. But did you know, trillions of tiny particles less than 5 millimeters in diameter are also floating around in there? These particles end up in the food chain. Sea plankton, which are an important source of food for fish and other marine animals, have been filmed eating them.

The ugly face of plastic pollution

An end in sight?

Tentative measures to cut down on disposable plastic have already been taken in some African countries with bans on plastic bags, while the European Union is looking into prohibiting single-use plastic products. But if current trends continue, scientists believe there will be 12 billion metric tons of plastic on the planet by 2050.